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Subject: Re: [PATCH v2] bluetooth, bpf: split sk_filter in l2cap_sock_recv_cb
From: Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <alpine.OSX.2.20.1607260839140.22879@mjmartin-mac01.local>
Date: Wed, 27 Jul 2016 13:35:41 +0200
Cc: Willem de Bruijn <willemb@google.com>,
	"open list:BLUETOOTH DRIVERS" <linux-bluetooth@vger.kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Gustavo Padovan <gustavo.padovan@collabora.co.uk>,
	Alexei Starovoitov <ast@kernel.org>
Message-Id: <F5CADE2F-FF8C-4EBD-A56D-1C35DCA7B654@holtmann.org>
References: <20160726000523.11189-1-mathew.j.martineau@linux.intel.com> <CA+FuTSc18TsLQQx5v0Wdkmk6ffqS+=vUVRHxBx6pyYtpxyk2Fw@mail.gmail.com> <alpine.OSX.2.20.1607260839140.22879@mjmartin-mac01.local>
To: Mat Martineau <mathew.j.martineau@linux.intel.com>
Sender: linux-bluetooth-owner@vger.kernel.org
List-ID: <linux-bluetooth.vger.kernel.org>

Hi Mat,

>>> I modified the original patch to call sk_filter for ERTM before the packet is
>>> handled by the state machine and to not set the filter locked flag. I tested
>>> using l2test in ERTM mode, with and without a "randomly drop 1 in 64 packets"
>>> filter attached.
>> 
>> Thanks for testing. For consistency's sake, is it preferable to filter
>> at this point for all modes?
> 
> Only ERTM and streaming mode end up on this code path, and I think there's a benefit to handling these two modes similarly. There are a number of other paths to l2cap_sock_recv_cb(), and there isn't one perfect place to call sk_filter for all modes.

would code restructuring help to create a better place to put sk_filter?

>>> 
>>> ---
>>> net/bluetooth/l2cap_core.c |  4 ++++
>>> net/bluetooth/l2cap_sock.c | 13 +++++++++++--
>>> 2 files changed, 15 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
>>> index 54ceb1f..d5de0ce 100644
>>> --- a/net/bluetooth/l2cap_core.c
>>> +++ b/net/bluetooth/l2cap_core.c
>>> @@ -32,6 +32,7 @@
>>> 
>>> #include <linux/debugfs.h>
>>> #include <linux/crc16.h>
>>> +#include <linux/filter.h>
>>> 
>>> #include <net/bluetooth/bluetooth.h>
>>> #include <net/bluetooth/hci_core.h>
>>> @@ -6610,6 +6611,9 @@ static int l2cap_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb)
>>>                goto drop;
>>>        }
>>> 
>>> +       if (chan->mode == L2CAP_MODE_ERTM && sk_filter(chan->data, skb))
>>> +               goto drop;
>>> +
>> 
>> sk_filter can also accept, but trim, packets. If the protocol expects
>> a header that it unconditionally pulls later, use sk_filter_trim to
> 
> sk_filter_trim_cap? I see that you added that recently. It's not in bluetooth-next and we're aiming for a patch that can be easily backported to stable.

Lets create a version that fixes this first. One version that we can backport into stable. And then we can start utilizing newer infrastructure available in Linus' tree.

Regards

Marcel